Clarify public WebSocket availability in Flashblocks docs

[dieutx]

Summary

Several Base docs pages currently imply that the public wss://*.base.org endpoints can be used directly for Flashblocks subscriptions.

What I observed

A WebSocket upgrade request to the public Base RPC endpoints returns 405 Method Not Allowed instead of establishing a subscription connection.

Impacted areas

• RPC overview
• eth_subscribe
• Flashblocks FAQ
• newFlashblocks
• newFlashblockTransactions
• pendingLogs

Suggested fix

Update the docs to clarify that:

• the public base.org RPC endpoints are currently HTTP-only
• subscription-based Flashblocks usage should go through a node provider or a self-hosted Flashblocks-aware node
• examples should avoid suggesting direct use of wss://mainnet-preconf.base.org